The invention relates to a flexible pipe used for trickle irrigation of plants and its manufacture by an extrusion process. It relates particularly to a plastic pipe provided with spaced-apart trickle irrigation emitter means integral with the pipe wall.
Conventional drip irrigation means consist of a pipe provided with a plurality of discrete emitter units which are inserted into, or otherwise fastened to the inside or the outside of the pipe wall by gluing or otherwise. There exist untold types of emitters, all having the common purpose of presenting a given resistance to the water flow, so as to reduce it to a trickle which serves to irrigate each of a plurality of spaced-apart plants by the same amount of water.
Practically all trickle irrigation emitters are characterized by a flow path in the shape of a long water duct of relatively wide cross section and of an intricate, preferably labyrinth pattern, with the aim to preventing clogging of the duct on the one hand, while, creating the required flow resistance, on the other hand.
It has been suggested to provide emitters which are incorporated in or with the pipe wall, for instance in the form of longitudinal cavities of a given length, communicating at their respective two ends with the pipe interior and the outside. Another kind of emitter pipe comprises a labyrinthine sleeve closely attached to the outside of the pipe wall and extending along it over a predetermined length.
In our Israeli Patent Specification No. 77875 we have disclosed a trickle irrigation pipe provided with evenly spaced emitters, which consist of an inner tube of an extruded plastics comprising a plurality of inwardly protruding, longitudinally spaced wells, and of an outer tube of the same or similar material covering the inner tube, whereby the wells are covered by the outer tube and thus form closed chambers. One flexible wafer each is movably positioned in each chamber, each wafer containing a flow-restricting duct on the side facing the outer tube and a passage extending through the wafer at a first end of the flow-restricting duct. The chamber communicates with the pipe interior through water inlet openings in its bottom portion, and with the atmosphere by means of a hole in the outer tube opposite the second end of the flow-restricting duct.
Water entering the chamber from the pipe through the inlet openings urges the flexible wafer towards the top portion of the chamber formed by the outer tube. Increasing water pressure deforms the wafer, thereby reducing the cross section of the flow-restricting duct. The material of the wafer and the shape and cross section of the duct are so selected that the water through-flow remains substantially constant for a given pressure range, say between 1 to 4 bars.
The pipe is manufactured by extruding the inner tube, impressing the wells into the still-soft tube wall, and perforating the bottom of the well at the same time to form a number of inlet openings; inserting a flexible wafer into each well and guiding the tube through a second extruder, effecting covering the inner tube together with the wells--which contain the flexible wafers--by an outer tube of the same material which fuses with the surface of the inner tube and completely unites with it to form a strong irrigation pipe. Water outlet holes are subsequently punched into the outer tube at the points of the outlet ends of the flow-restricting ducts in the water surfaces.
Although each of the trickle emitters along a pipe emits a uniform water output, it has been experienced that the outputs of different emitters along the pipe differ from each other, and it was found that these different outputs were caused by the different configuration of the chamber top formed by the tubular cover. The outer tube sometimes covers the chamber in cylindrical shape and on the other occasions is stretched flat across the wells, thus forming planar chamber tops. The different shapes influence the deformation of the flexible wafers and of the flow-restricting ducts and, accordingly, the water output of differently deformed wafers.
It is, therefore, the main object of the present invention to provide a uniform contact surface for the flexible wafers, thus ensuring uniform deformation of each wafer and each flow restricting duct, while retaining the principle of the double-walled pipe and of the closed chamber incorporated in the pipe wall between an outer and an inner tube fused together.